Pathogenesis of Herpes simplex virus infections in guinea pigs

Models of Herpes Simplex Virus Latency

Our current understanding of HSV latency is based on a variety of clinical observations, and in vivo, ex vivo, and in vitro model systems, each with unique advantages and drawbacks. The criteria for authentically modeling HSV latency include the ability to easily manipulate host genetics and biological pathways, as well as mimicking the immune response and viral pathogenesis in human infections. Although realistically modeling HSV latency is necessary when choosing a model, the cost, time requirement, ethical constraints, and reagent availability are also equally important. Presently, there remains a pressing need for in vivo models that more closely recapitulate human HSV infection. While the current in vivo, ex vivo, and in vitro models used to study HSV latency have limitations, they provide further insights that add to our understanding of latency. In vivo models have shed light on natural infection routes and the interplay between the host immune response and the virus during latency, while in vitro models have been invaluable in elucidating molecular pathways involved in latency. Below, we review the relative advantages and disadvantages of current HSV models and highlight insights gained through each.

Nonclinical safety evaluation of two vaccine candidates for herpes simplex virus type 2 to support combined administration in humans

Herpes simplex virus type 2 (HSV-2) is the most common cause of genital disease worldwide. The development of an effective HSV-2 vaccine would significantly impact global health based on the psychological distress caused by genital herpes for some individuals, the risk transmitting the infection from mother to infant, and the elevated risk of acquiring HIV-1. Five nonclinical safety studies were conducted with the replication defective HSV529 vaccine, alone or adjuvanted with GLA-SE, and the G103 subunit vaccine containing GLA-SE. A biodistribution study was conducted in guinea pigs to evaluate distribution, persistence, and shedding of HSV529. A preliminary immunogenicity study was conducted in rabbits to demonstrate HSV529-specific humoral response and its enhancement by GLA-SE. Three repeated-dose toxicity studies, one in guinea pigs and two in rabbits, were conducted to assess systemic toxicity and local tolerance of HSV529, alone or adjuvanted with GLA-SE, or G103 containing GLA-SE. Data from these studies show that both vaccines are safe and well tolerated and support the ongoing HSV-2 clinical trial in which the two vaccine candidates will be given either sequentially or concomitantly to explore their potential synergistic and incremental effects.

Antiviral activity of PHA767491 on Caprine alphaherpesvirus 1 in vitro

Caprine alphaherpesvirus 1 (CpHV-1) induces genital lesions in its natural host similar to those caused by Human alphaherpesvirus 2 (HHV-2), commonly named herpes simplex virus 2 (HSV-2) in human patients. CpHV-1 infection in goats could represent a useful homologous animal model for the study of HSV-2 infection, chiefly for the assessment of antiviral drugs in in vivo studies. PHA767491 is a potent inhibitor of HSV-1 and HSV-2, being able to limit replication of HHVs both in vitro and in the mouse model. In the present study the antiviral efficacy of PHA767491 against CpHV-1 was evaluated in vitro in MDBK cells. PHA767491 inhibited significantly CpHV-1 replication in a dose-dependent fashion by up to 2.50 log10 TCID₅₀/50 μl and was able to decrease viral DNA by nearly 8 log10. These findings confirm that PHA767491 is highly effective not only against simplexviruses (HSV-1 and HSV-2), but also against the varicellovirus CpHV-1. Experiments will be necessary to assess whether PHA767491 is suitable for treatment of vaginal lesions in CpHV-1-goat model. This could provide hints for the therapy of genital alphaherpesvirus infections in humans.

Virucidal activity of ginger essential oil against caprine alphaherpesvirus-1

The emergence of alphaherpesvirus strains resistant to commonly used antiviral drugs has prompted the research for alternative, biologically active anti-herpetic agents. Essential oils (EOs) have shown anti-infective properties against human herpes simplex viruses (HSV-1 and -2). Caprine alphaherpesvirus 1 (CpHV-1) induces genital lesions in its natural host and it is regarded as a useful homologous animal model for the study of HSV-2 infection, chiefly for the assessment of antiviral drugs in in vivo studies. In the present study we evaluated the activity in vitro of ginger EO (GEO) against CpHV-1. GEO was found to be effective as virucide on cell-free virus, inactivating CpHV-1 up to 100%. The virucidal activity of GEO is likely accounted for by disruption of herpesvirus envelope and its associated structures which are necessary for virus adsorption and entry into host cells. On the opposite, GEO was not able to inhibit virus adsorption and/or replication, as treatment of cells before and after infection did not abolish virus infectivity. GEO could be suggested for topical applications in in vivo experiments using CpHV-1/goat model, since the lipophilic nature of EOs favours their adsorption through the cutaneous/mucosal barrier, either alone or in conjunction with other molecules. These findings open several perspectives in terms of therapeutic possibilities for a number of human and animal alphaherpesviruses.

The Characteristics of Herpes Simplex Virus Type 1 Infection in Rhesus Macaques and the Associated Pathological Features

As one of the major pathogens for human herpetic diseases, herpes simplex virus type 1 (HSV1) causes herpes labialis, genital herpes and herpetic encephalitis. Our aim here was to investigate the infectious process of HSV1 in rhesus macaques and the pathological features induced during this infection. Clinical symptoms that manifested in the rhesus macaque during HSV1 infection included vesicular lesions and their pathological features. Viral distribution in the nervous tissues and associated pathologic changes indicated the typical systematic pathological processes associated with viral distribution of HSV1. Interestingly, vesicular lesions recurred in oral skin or in mucosa associated with virus shedding in macaques within four to five months post-infection, and viral latency-associated transcript (LAT) mRNA was found in the trigeminal ganglia (TG) on day 365 post-infection. Neutralization testing and enzyme-linked immunospot (ELISpot) detection of specific T cell responses confirmed the specific immunity induced by HSV1 infection. Thus, rhesus macaques could serve as an infectious model for HSV1 due to their typical clinical symptoms and the pathological recurrence associated with viral latency in nervous tissues.

In vitro and in vivo antiherpetic effects of (1R,2R)-1-(5'-methylful-3'-yl)propane-1,2,3-triol

In this study, we demonstrated the in vitro and in vivo antiherpetic activities of a stable furan derivative, (1R,2R)-1-(5'-methylful-3'-yl)propane-1,2,3-triol (MFPT), which had originally been isolated from Streptomyces sp. strain FV60. In the present study, we synthesized MFPT from (5-methylfuran-3-yl)methanol in 6 steps for use in the experiments. MFPT showed potent in vitro antiviral activities against two acyclovir (ACV)-sensitive (KOS and HF) strains and an ACV-resistant (A4-3) strain of herpes simplex virus type 1 (HSV-1) and an ACV-sensitive HSV type 2 (HSV-2) UW 268 strain, their selectivity indices ranging from 310 to 530. By intravaginal application of MFPT to mice, the virus yields decreased dose-dependently against the three strains of HSV-1 and HSV-2. When MFPT was applied at a dose of 1.0 mg/day, the lesion scores, as clinical signs manifested by viral infection, were extensively suppressed in HSV-1-infected mice, whereas the lesion scores in HSV-2-infected mice were not markedly decreased. Interestingly, MFPT exerted an inhibitory effect against ACV-resistant HSV-1 in mice to a similar degree as in ACV-sensitive HSV-1-infected mice. Therefore, the compound might have potential for developing a topical antiviral agent that could be also applied to the infections caused by ACV-resistant viruses.

DNA cleavage enzymes for treatment of persistent viral infections: recent advances and the pathway forward

Treatment for most persistent viral infections consists of palliative drug options rather than curative approaches. This is often because long-lasting viral DNA in infected cells is not affected by current antivirals, providing a source for viral persistence and reactivation. Targeting latent viral DNA itself could therefore provide a basis for novel curative strategies. DNA cleavage enzymes can be used to induce targeted mutagenesis of specific genes, including those of exogenous viruses. Although initial in vitro and even in vivo studies have been carried out using DNA cleavage enzymes targeting various viruses, many questions still remain concerning the feasibility of these strategies as they transition into preclinical research. Here, we review the most recent findings on DNA cleavage enzymes for human viral infections, consider the most relevant animal models for several human viral infections, and address issues regarding safety and enzyme delivery. Results from well-designed in vivo studies will ideally provide answers to the most urgent remaining questions, and allow continued progress toward clinical application.

HSV-2 vaccine: current state and insights into development of a vaccine that targets genital mucosal protection

HSV-2 is one of the most prevalent sexually transmitted infections that result in significant morbidity and financial burden on health systems around the world. Recurrent and asymptomatic re-activation accompanied by viral shedding is common among sero-positive individuals, leading to relatively high efficiency of transmission. Prophylactic HSV-2 vaccines are the best and cheapest option to address the problems associated with HSV-2 infections globally. However, despite persistent efforts, the search for an efficacious vaccine for HSV-2 remains elusive. In this review, the current state of HSV-2 vaccines and the outcome of past human trials are examined. Furthermore, we discuss the evidence and strategies from experimental mouse models that have been successful in inducing protective immunity in the genital tract against HSV-2, following immunization. Future vaccination strategies that focus on induction of robust mucosal immunity in the genital tract may hold the key for a successful vaccine against HSV-2.

Of mice and not humans: how reliable are animal models for evaluation of herpes CD8(+)-T cell-epitopes-based immunotherapeutic vaccine candidates?

Herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2)-specific CD8(+) T cells that reside in sensory ganglia, appear to control recurrent herpetic disease by aborting or reducing spontaneous and sporadic reactivations of latent virus. A reliable animal model is the ultimate key factor to test the efficacy of therapeutic vaccines that boost the level and the quality of sensory ganglia-resident CD8(+) T cells against spontaneous herpes reactivation from sensory neurons, yet its relevance has been often overlooked. Herpes vaccinologists are hesitant about using mouse as a model in pre-clinical development of therapeutic vaccines because they do not adequately mimic spontaneous viral shedding or recurrent symptomatic diseases, as occurs in human. Alternatives to mouse models are rabbits and guinea pigs in which reactivation arise spontaneously with clinical herpetic features relevant to human disease. However, while rabbits and guinea pigs develop spontaneous HSV reactivation and recurrent ocular and genital disease none of them can mount CD8(+) T cell responses specific to Human Leukocyte Antigen- (HLA-)restricted epitopes. In this review, we discuss the advantages and limitations of these animal models and describe a novel "humanized" HLA transgenic rabbit, which shows spontaneous HSV-1 reactivation, recurrent ocular disease and mounts CD8(+) T cell responses to HLA-restricted epitopes. Adequate investments are needed to develop reliable preclinical animal models, such as HLA class I and class II double transgenic rabbits and guinea pigs to balance the ethical and financial concerns associated with the rising number of unsuccessful clinical trials for therapeutic vaccine formulations tested in unreliable mouse models.

Highly virulent strains of herpes simplex virus fail to kill mice following infection via gingival route

Virulence of herpes simplex virus (HSV) in mice has been demonstrated to be dependent on the site of infection. In this experiment, pathogenesis of HSV was studied in 2 different routes of infection in a mouse model system. When BALB/c mice were infected with 5 x 10(3) plaque-forming units (PFU) of virulent HSV type 1 Miyama GC+ strain (HSV-1-GC+) intraperitoneally, all mice were dead in 6 to 9 days. HSV-1-GC+ was recovered from organs such as the cerebrum, cerebellum, brainstem, and spleen 2 to 5 days after infection, but not from other organs such as trigeminal ganglia. However, if mice were infected in the maxillary gingiva with 1.0 x 10(7) PFU of HSV-1-GC+, all mice survived. HSV-1-GC+ was recovered from the trigeminal ganglia and brainstem 2 to 5 days after infection, but not from other organs tested. When mice were infected in maxillary gingiva with HSV-1-GC+, followed by the intraperitoneal injection of 6 mg of cyclophosphamide 72 hrs after virus infection, all mice were dead within days. Immunofluorescent and hematoxylin-eosin staining of gingival tissue sections revealed that when mice were infected in maxillary gingiva with HSV-1-GC+, 3 times as many gamma delta T-cells and 5 times as many polymorphonuclear cells can be detected in sections of maxillary gingiva when compared with non-infected mice. These data show that the gingiva of mice is considerably more resistant to infection with HSV, compared with the peritoneal cavity, and suggest the possible presence of an oral defense mechanism which might be different from that in the peritoneal cavity.

Outcome of herpes simplex virus type 2 infection in guinea pigs

Factors that influence the outcome of genital herpes simplex virus (HSV) infection were explored in a guinea pig model. The viral inoculum required to establish infection in 50% of animals (ID50) was similar for inbred (strain 2) and outbred (Hartley) guinea pigs. However, the viral inoculum required to produce clinical disease in 50% of the animals (CD50) was 10 times greater for strain 2 compared to Hartley animals. HSV infection of both inbred and outbred animals was more likely to result in death of weanling than adult animals. The duration and severity of genital disease and the magnitude of vaginal viral replication were similar for strain 2 and Hartley animals in both young and adult animals. The lethal dose for 50% of animals (LD50) was 100-fold greater than the CD50 for Hartley animals, but the LD50 and the CD50 were equal in strain 2 guinea pigs. Viral cultures of homogenized neural tissues from infected animals revealed that HSV ascended to the level of the temporal cortex in strain 2 guinea pigs while virus was never recovered above the lumbar spinal cord in Hartley animals. Endogenous peripheral blood mononuclear cell-mediated cytolytic activity against HSV-infected targets was greater prior to HSV inoculation in survivors compared to animals that died. A fatal outcome of genital HSV-2 may relate to the failure to limit CNS viral replication. Death is more common among guinea pigs that have low endogenous HSV-directed natural killer activity, such as occurs among strain 2 and young animals whether inbred or outbred.

Efficacy of HSV-1 ISCOM vaccine in the guinea-pig model of HSV-2 infection

The capability of a herpes simplex virus (HSV)-1 ISCOM vaccine to protect against intravaginal HSV-2 challenge infection in guinea-pigs is described. The protective efficacy of the HSV-1 ISCOM vaccine is compared with that of a purified, aqueous HSV-1 antigen preparation administered using a similar immunization schedule. The results show that female guinea-pigs immunized with two doses of HSV-1 ISCOM vaccine, each consisting of 20 micrograms of protein given 2 weeks apart responded with high ELISA and neutralization antibody titres, and are almost completely protected against the clinical effects of intravaginal challenge with 10(5.2) TCID50 of HSV-2. This cross-protection is significantly greater than that observed in guinea-pigs immunized with a single dose of HSV-1 ISCOM vaccine, two doses of aqueous HSV-1 antigen preparation or two doses of a mock ISCOM vaccine. However, none of the vaccine preparations completely prevented HSV-2 replication following challenge. Western blot and radioimmunoprecipitation of sera from immunized guinea-pigs show the HSV-1 ISCOM vaccine preparation to contain the major HSV-1 glycoproteins. These findings are discussed in relation to the value and potential use of HSV-1 ISCOM vaccine in humans.

Protection and serum antibody responses in guinea-pigs and mice immunized with HSV-1 antigen preparations obtained using different detergents

Guinea-pigs immunized with a zwitterionic detergent-extracted HSV-1 antigen preparation responded with EIA and NT serum antibody titres that were significantly greater than those elicited by a non-ionic detergent-extracted antigen preparation inoculated using a similar dosage schedule. Following intravaginal challenge of the guinea-pigs with HSV-2 (strain SH/B), there was no statistically significant difference in the protection afforded to these animals by the two antigen preparations, although the results indicated the zwitterionic detergent-extracted HSV-1 antigen preparation to be slightly superior in this respect. In mice, the zwitterionic detergent-extracted HSV-1 antigen preparation elicited an EIA antibody response and partial protection against homologous virus challenge. The relevance of these animal models to determination of immunogenicity and efficacy of HSV vaccines prepared for use in man, and the reasons for the differences in immunogenicity of these HSV-1 antigen preparations in guinea-pigs, are discussed.

Effect of L-lysine monohydrochloride on cutaneous herpes simplex virus in the guinea pig

The effect of topical applications of crystalline lysine therapy on cutaneous herpes simplex virus (HSV) inoculations and subsequent dorsal root ganglia (DRG) infection was studied in male Hartley guinea pigs. Although HSV-I was recovered from the inoculated sites from all animals, the L-lysine-treated skin remained clinically normal, whereas untreated controls manifested clinical symptoms up to 3 days postinoculation (p.i.). However, cocultivation of DRG (C1-S1) indicated a selective tropism of infective particles to specific DRG in the groups treated with amino acids. In lysine-treated animals, HSV was recovered from a few DRG (T-12, T-13, and L-1) at 3 days p.i. and from DRG T-10 in leucine-treated controls; yet no HSV was recovered from DRG of untreated controls. These results suggest an immunomodulatory effect of L-lysine on inoculation site infections and the possible potentiation of subsequent DRG manifestation in amino-acid-treated animals.

A test for the relative potency of herpes simplex virus vaccines based upon the female guinea-pig model of HSV 2 genital infection

An ELISA for total herpes simplex virus (HSV) 1 antigen content and a test of immunogenicity based upon the female guinea-pig model of HSV 2 genital infection were applied to two samples from batches of HSV 1 subunit ('Skinner') vaccine. The ELISA was reproducible within an approximately threefold limit of error and batches 1 and 2 were indistinguishable in antigen content. The effects of vaccination in the guinea-pig model were assessed by a statistical analysis of scores derived from the principal clinical signs, vaginal oedema and lesions on the external genitalia. The statistical power of the guinea-pig assay was such that reductions in the severity of illness approaching 40% would be significant (P less than 0.05) on 90% of occasions. The ability to make quantitative estimates of immunogenicity will prove useful in the quality control of HSV vaccine batches which are destined for clinical trials in man.

Neurovirulence of individual plaque stocks of Herpes simplex virus type 2 strain HG 52

The virulence of ten independent plaque stocks of HSV-2 strain HG 52 was determined by intracranial inoculation of 3 week old BALB/c mice. The ten stocks exhibited a range of LD50 which could be grouped into three classes; high (less than 10(3) pfu/mouse), intermediate (10(3)-10(4) pfu/mouse) and low (greater than 10(5) pfu/mouse). Analysis of the ten stocks using six different restriction endonucleases showed no significant variation in the size and distribution of fragments. Isolates from the brains of dead mice had restriction enzyme profiles indistinguishable from the initial infecting virus. The pfu:particle ratios of the virus stocks were comparable. There were no significant differences between the single growth cycle characteristics in vitro of the parental HG 52 and the various plaque purified stocks. In vivo after intracranial inoculation the low virulence stocks grew poorly while those of high virulence grew well. Plaques were picked from the high and low virulence stocks after passage five times in vitro and re-assayed for virulence. In some cases there were differences in the LD50s of passaged plaque isolates from that of parental stock. The restriction enzyme profiles of the passaged plaque isolates remained unchanged. The analysis has clearly demonstrated virulence heterogeneity within a single HSV-2 virus stock.

Enhanced in vitro reactivation of latent herpes simplex virus from neural and peripheral tissues with hexamethylenebisacetamide

We evaluated the effect of the demethylating agent hexamethylenebisacetamide on reactivation of latent herpes simplex virus type 2 (HSV-2) from guinea pig neural and extraneural tissues. Four explant cultures from the dorsal root ganglia of 42 latently infected guinea pigs and vaginal and cervical explant cultures from 33 animals were divided so that half received 5 mM of hexamethylenebisacetamide supplemented media and half media alone. HSV-2 was recovered earlier and from a greater percentage of treated cultures than controls. For example, seven days after explant, HSV-2 was recovered from 35 of 84 (42%) treated dorsal root ganglia cultures compared to seven of 84 control cultures (p less than 0.0001). Likewise, HSV-2 was recovered seven days after explant from 11 of 66 (17%) treated external genital skin cultures and 2 of 66 control cultures (p less than 0.009), Hexamethylenebisacetamide had no effect on productive HSV-2 infection in guinea pig dorsal root ganglia cultures. This study provides evidence for a role of demethylation in the reactivation of latent HSV from neural as well as peripheral tissues and suggests that latent virus exists at these sites in a similar state. Hexamethylenebisacetamide should be useful in studies of herpes virus latency because it decreases the time necessary to recover virus from latently infected tissues and enhances the recovery of virus.

Hamster model for herpes simplex virus infection of the central nervous system

Adult Syrian hamsters were inoculated with a mouse brain passage of herpes simplex virus type 1 (HSV-1) along an intradermal and an oral route after local scarification. For both routes, clinical symptoms of central nervous system (CNS) involvement were seen in the period between five and 12 days post infection. Compared with the route via the buccal mucosa, CNS involvement by intradermal infection is easier to establish. With a minimum dose of 2 X 10(4) TCID50 virus via the intradermal route, an infection rate of 80% or more can be obtained reproducibly and detected simply by clinical observation without need of a survey of the humoral immune response. Scarification of the skin prior to inoculation was found to be essential for establishment of the CNS infection.

Herpes simplex virus type 1 persistence and latency in cultured rabbit corneal epithelial cells, keratocytes, and endothelial cells

Cell cultures of rabbit corneal epithelium, keratocytes, and endothelium were used to determine the lytic cycle of herpes simplex virus type 1. Viral growth was fastest in epithelial cells. A novel HSV-1 in-vitro latency system was established in the three distinct cell types. Cell cultures were inoculated at low multiplicities of infection with HSV-1. Temperature manipulation alone was used to induce and reactivate latent HSV-1 infections. The presence of cellular stress proteins was demonstrated at supraoptimal temperatures. All cell types were capable of maintaining latent viral infections under these conditions. Viral persistence was present in 20% of epithelial cell cultures at supraoptimal temperatures, but not in keratocyte cultures or endothelial cell cultures.

Antiviral activity of 5-ethyl-2'-deoxyuridine against herpes simplex viruses in cell culture, mice, and guinea pigs

The susceptibility of 3 laboratory strains and 24 clinical isolates of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) to 5-ethyl-2'-deoxyuridine was determined in plaque reduction assays in Vero cells. The median effective doses were 8.6 and 7.8 microM, respectively. The drug was less potent than acyclovir and other related antiviral drugs, but it had a high therapeutic index against both HSV-1 and HSV-2. Drug-resistant viruses were readily produced in cell culture. These variants were cross-resistant to acyclovir, 2'-fluoro-5-iodoaracytosine, and 2'-fluoro-5-methylarauracil but were susceptible to vidarabine or phosphonoformate. These findings confirm that the selective antiviral activity of 5-ethyl-2'-deoxyuridine is mediated by the virus-induced thymidine kinase. Oral or intraperitoneal administration of the drug at nontoxic doses was ineffective in protecting mice against intracerebral challenge with virus. Using implanted osmotic minipumps or coadministering the drug with dimethyl sulfoxide failed to decrease the mortality rate. In guinea pigs infected genitally with HSV-2, topical drug treatment was more effective than placebo in reducing lesion severity and other clinical and virological variables. These effects were noted whether the drug treatment was initiated 3 or 24 h after infection (ascertained serologically). Drug-treated animals had a significantly lower herpes antibody titer than did placebo-treated guinea pigs, suggesting that the drug can also reduce the viral antigen load. In this model, the drug appeared to be as effective as topical phosphonoformate or acyclovir.

Dissemination of herpes simplex virus in ganglia after footpad inoculation in neurectomized and non-neurectomized mice

After unilateral footpad inoculation with herpes simplex virus (HSV) the infection spreads initially to the ipsilateral and afterwards to the contralateral spinal ganglia. In about 25 percent of the mice the virus also reaches the trigeminal ganglia. Furthermore, we have shown that only a complete severance of the nervous connections can prevent the colonization of ganglia with HSV after footpad inoculation. Results of previous experiments in which only the sectioning of the sciatic nerve was able to prevent the invasion of ganglia, are difficult to explain. It appears also that HSV travels in the nerve toward the ganglia in a non-infectious form, and that the infectious virus detectable in nerves originates not from the peripheral inoculation site, but from the infectious virus pool which accumulates in spinal ganglia. A limited role of the circulatory system in the colonization of sensory ganglia by HSV cannot be excluded, since in a few cases virus was detected in ganglia after sectioning of both the sciatic and the femoral nerve.

Sensitivity of oral tissues to herpes simplex virus--in vitro

Epithelial and fibroblast cells from the human gingival sulcus area were cultivated in vitro, and their sensitivity to the herpes simplex virus (HSV) was studied. Fibroblasts were sensitive to HSV infection and supported virus multiplication as evidenced by nuclear inclusion bodies and a cytopathogenic effect. Epithelial cells which were primarily devoid of HSV antigens were infected with HSV as demonstrated by positive immunofluorescent staining and damage to the cells at a later stage. Epithelial cells that were found to harbor HSV antigens upon removal from the patients prior to infection in vitro, maintained these antigens throughout the period of in vitro cultivation. The sensitivity of both epithelial cells and fibroblasts from the gingival sulcus area to HSV infection in vitro is significant for the understanding of the role of these tissues as a primary site of infection and as a possible reservoir for the latent virus between recurrences.

Animal studies on the efficacy of vaccination against recurrent herpes

Guinea pigs, latently infected with herpes simplex virus type 2 (HSV 2), were immunized with an HSV 2 vaccine derived from extracts of infected cells and either formol inactivated or detergent treated. Although such postinfection vaccination could significantly increase the titers of neutralizing antibodies, it had no effect on the course of recurrent herpes in these animals.